1. Field of the Invention
The present invention relates to a method and arrangement for correction of the evaluation of a switching threshold of a magnetic sensor, especially for analysis of motion of a transmitter wheel, in which switching edges of a sensor signal are evaluated and the magnetic sensor outputs a signal when the switching edges exceed or drop below a predetermined threshold value.
2. Related Art
So-called active rotation sensors and position sensors, as are used e.g. or control of motors or also in transmission and vehicle dynamics control in motor vehicles, are known. These sensors operate as phase transmitters, rotation speed transmitters or as so-called rotation speed sensors. The integrated circuits used in connection with these sensors for detection and evaluation, e.g. the so-called sensor ASICs, produce an electrical pulse edge from each magnetic pulse edge. That is a change of a binary output signal from Low to High or the reverse occurs or an electrical pulse of a definite length is produced.
Magnetic sensor arrangements are known in themselves, which for example operate with fixed threshold values. These sensor circuits have fixed threshold values which cannot be corrected and which produce errors due to transmitter wheel defects that are reproduced in the output signal. On the other hand, there are so-called self-calibrating sensors, which determine the minima and maxima of the measured values and then correct their circuit thresholds, e.g. by determining a general or overall average value. However faults in the transmitter wheel change the amplitudes of extrema, which are derived for determination of the switching threshold correction and produce errors in the output signals of these sensors.
Furthermore programmable sensors are known, in which a turn-on-switching threshold and a position of the desired switching threshold between the magnetic extrema can be programmed non-volatile in addition to the self-calibration. Both occur integrally for the entire transmitter wheel. Also in this case eccentricities in the transmitter wheel cause angle errors in the output signal of the sensor.
For all these prior art cases some transmitter wheel faults, such as pitch errors or graduation errors in multiple wheels or also eccentricities, e.g. of camshaft transmitter wheels, cannot be corrected.
For example an arrangement for contactless rotation angle determination by means of a pulse-generating wheel is described in DE 197 50 304 A1. In this arrangement rotation direction detection is possible, whereby a change of spacing of the pulse generating elements is performed in one rotation direction and thus the key ratio changes.